1. Field of the Invention
The disclosed concept relates generally to a system structured to position a domer assembly so that a reciprocating ram is substantially concentrically aligned with a die pack during the return stroke of a ram and, more specifically, to a positioning system structured to detect the position of the ram during the reciprocal motion and to move the domer assembly dynamically.
2. Background Information
Generally, an aluminum can begins as a sheet of aluminum from which a circular blank is cut. The blank is formed into a “cup” having a bottom and a depending sidewall. The cup is fed into a bodymaker which passes the cup through additional circular dies that thin and elongated the cup. That is, the cup is disposed in front of the punch mounted on an elongated ram. The ram is structured to reciprocate and pass the cup through the circular dies which (re)draw and iron the cup. That is, on each forward stroke of the ram, a cup is passed through the circular dies which further form the cup into a can body. On the return stroke, the now elongated can body is removed from the ram and a new cup is disposed thereon. Following additional finishing operations, e.g. trimming, washing, printing, etc., the can body is sent to a filler which fills the can with product. A top is then coupled to, and sealed against, the can body, thereby completing the can.
More specifically, the die pack in the bodymaker has multiple, spaced dies, each die having a substantially circular opening. Each die opening is slightly smaller than the next adjacent upstream die. Thus, when the punch draws the cup through the first die, the redraw die, the aluminum cup is deformed over the substantially cylindrical punch. Because the openings in the subsequent dies in the die pack have a smaller inner diameter, i.e. a smaller opening, the aluminum cup is thinned as the ram moves the aluminum through the rest of the die pack. The space between the punch and the redraw die is typically less than about 0.010 inch and less than about 0.004 inch in the last ironing die. After the can has moved through the last die, the cup bottom and sidewall have the desired thickness; the only other deformation required is to shape the bottom of the cup into an inwardly extending dome.
That is, the distal end of the punch is concave. At the maximum extension of the ram is a “domer.” The domer has a generally convex dome and a shaped perimeter. As the ram reaches its maximum extension, the bottom of the can body engages the domer and is deformed into a dome and the bottom perimeter of the can body is shaped as desired; typically angled inwardly so as to increase the strength of the can body and to allow for the resulting cans to be stacked. As the ram withdraws, the can body then is stripped off of the end of the punch by injecting air into the center of the ram. The air comes out of the end of the punch and breaks the can body loose from the punch. Typically, there is also a mechanical stripper, which prevents the can body from staying on the punch it retracts back through the tool pack. The ram is withdrawn through the die pack, a new cup is deposited on the punch and the cycle repeats.
The ram and the die pack are typically oriented generally horizontally. This orientation, however, allows for wear and tear on the punch. That is, the dies in the die pack must be separated so as to allow for the proper deformation of the cup. This means that the ram must extend horizontally through the entire die pack; a distance that may be anywhere from 18 to 30 inches. This is also the stroke length for the bodymaker. This means that the ram is, essentially, a cantilevered arm. As is known, even a very rigid member supported as a cantilever will droop at the distal end. While this droop is generally not a problem for stationary members, the droop is a problem for a reciprocating ram passing through a die with a radial clearance of less than about 0.004 inch between the punch and the die. Typically, the domer is statically aligned to the punch, in order to compensate for the droop, however this alignment may not be correct for the dynamics of the ram in the machine. Also, there are other factors that can cause the punch not to run concentrically to the machine center line. Thus, because of the droop and other reasons, the ram may not be concentric with the circular dies, i.e. ram is closer to, or in contact with, the lower portion of the die. Over time, the contact between the punch and the die causes either of both to become damaged. When this happens, the damaged parts must be replaced. Further, because this is a time consuming procedure, and because a typical can forming machine produces over 15,000 cans an hour, having a misaligned ram is a disadvantage. That is, if the ram is misaligned, it is unlikely that any cans will be made. The ram should be aligned to the centerline of the machine (horizontally and vertically).
The position of the ram is also affected by the position of the domer. That is, the ram is brought into engagement with the domer and, if the domer is not properly aligned, will cause the ram to vibrate or otherwise be misaligned with the die pack. Given the narrow spacing between the punch and the dies, even a slight misalignment or slight vibration, may cause the punch to contact the dies. Generally, the domer is mounted on an adjustable assembly. Prior to using the can forming machine, and as part of regular maintenance, the domer is manually aligned with the ram. That is, the ram is placed at, or near, its maximum extension and the domer is aligned with the punch. This method, however, does not solve the problem of abnormal wear on the punch due to contact with the dies. That is, the position of the ram/punch at rest may not be the same as the position of the ram/punch in motion. Thus, a stated problem with the known systems and methods for aligning a punch with a die assembly is that the known systems and methods do not detect the position of the punch in motion.